1. Field of the Invention
The present invention pertains to a valve assembly used to control the flow of a fluid, such as, without limitation, a flow of breathing gas in a user interface device, and, in one or more particular embodiments, to an anti-asphyxia valve for use in a user interface device structured to deliver a flow of breathing gas to a user to treat a sleep disorder breathing condition such as obstructive sleep apnea (OSA).
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without incubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver positive airway pressure (PAP) therapy to treat certain medical disorders, the most notable of which is OSA. Known PAP therapies include continuous positive airway pressure (CPAP), wherein a constant positive pressure is provided to the airway of the patient in order to splint open the patient's airway, and variable airway pressure, wherein the pressure provided to the airway of the patient is varied with the patient's respiratory cycle. Such therapies are typically provided to the patient at night while the patient is sleeping.
Non-invasive ventilation and pressure support therapies as just described involve the placement of a patient interface device including a mask component having a soft, flexible cushion on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal cushion having nasal prongs that are received within the patient's nares, a nasal/oral mask that covers the patient's nose and mouth, or a full face mask that covers the patient's face. Such patient interface devices may also employ other patient contacting components, such as forehead supports, cheek pads and chin pads. The patient interface device is connected to a gas delivery tube or conduit and interfaces the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such devices on the face of a wearer by a headgear having one or more straps adapted to fit over/around the patient's head.
Anti-asphyxia features (AAF) used in conjunction with OSA therapy are typically required as a safety device in masks that cover the nose and mouth. During respiratory therapy, should pressure no longer become available due to a power outage or a pump failure in the ventilator or pressure support device, for example, the patient will continue to be able to breathe with the use of an AAF. Typical designs in the market place take on primarily two configurations.
The first configuration employs a flap-style valve typically positioned within the fluid coupling conduit (e.g. elbow connector) of the mask. Such a flap style valve is fundamentally a reed style check valve. As the pressure from the ventilator or pressure support device is applied, the flap style valve opens, allowing air flow to the patient while blocking an exhaust cavity on the opposite side of the flap of the flap style valve. When no pressure comes from the ventilator or pressure support device, the flap seats and allows exhalation and inhalation at atmospheric pressure through a hole to atmosphere. The flap also serves to prevent the patient from pulling air from the volume of air in the gas delivery tubes and the ventilator or pressure support device.
The second configuration employs what is commonly called a Duck-bill valve. Duck bill valves are frequently used in industrial applications where low pressure drops are required. A duck bill valve is fundamentally two symmetrically opposed reed valves (i.e., two symmetrically opposed flaps). As pressure is applied from the ventilator or pressure support device, the two flaps open in opposite directions and seal off exhaust holes provided on each side of the valve. When no pressure comes from the ventilator or pressure support device, the flaps seat with one another and allow exhalation and inhalation at atmospheric pressure through the open exhaust holes. The flap also serves to prevent the patient from pulling air from the volume of air in the gas delivery tubes and the ventilator or pressure support device.
At least two current development trends within the design of masks for non-invasive ventilation and pressure support therapies are impacting the required functionally of supporting components, such as AAF devices, used therewith. These trends are the implementation of smaller gas delivery tubing (e.g., 15 mm inside diameter) and newer, under-the-nose style mask profiles. These features require a balancing of the necessary effective flow area to limit the pressure drop across the AAF while maintaining a smaller package profile. Achieving such balancing has proven to be challenging in connection with AAFs having one of the two prior art configurations described above.